1. Field of the Invention
The present invention is related to a cycle rim and a cycle wheel comprising such a rim.
More specifically, the invention is related to a rim and a wheel provided to receive a tire, and optionally an inner tube on the interior of the tire. The invention is not related to rims provided to receive a tubular (i.e., "sew-up"), which use rims formed from a pipe that is bent lengthwise and in cross-section.
2. Description of Background and Relevant Information
The rims adapted to receive a pneumatic tire have in a known manner a form having an axis of revolution. They have in cross-section two spaced lateral wings that form the lateral sides of the rim. The wings are joined in their lower portion by a lower bridge, and in their median portion by an upper bridge. The two bridges and the lower portion of the wings form a kind of a casing. The bridges of the casing are bored with a plurality of holes for the passage of wheel spokes. Preferably, the holes are equipped with eyelets mounted by crimping, which improve the linkage between the spokes and the rim.
The casing contributes to the flexional and torsional rigidity of the rim and determines the rigidity and the vertical resistance of the wheel, as well as its rigidity and lateral resistance.
Beyond the upper bridge, the wings extend so as to form with the upper surface of the upper bridge an annular cavity provided to receive the tire, and most often an inner tube. Preferably, the tip of the wings has a bead against which the tire rests, which improves its retention in the groove.
The rims currently available on the market are generally manufactured from a bent sectional bar of aluminum alloy whose both ends are butt-joined, by welding or drawing of a linkage sleeve, or any other appropriate means.
Important physical characteristics to consider in the design of a rim are the weight and the inertial moments of the rim with respect to the neutral axis passing through its center and perpendicular to the direction of a vertical deformation and the axis passing through its center and perpendicular to the direction of a lateral deformation. These physical characteristics are related to the material used and to the dimensions of the rim.
The dimensions of the rims are relatively set. Indeed, the dimensions of the upper cavity are determined from the usual dimensions of pneumatic tires. As for the dimensions of the walls of the casing, they are determined by the desired physical characteristics to be obtained. They likewise take into account the forces generated by the tension of the spoke. Another constraint taken into account is the extrusion of the sectional bar which is to make up the rim, and the joining of its two ends after bending. Indeed, it is known that the extrusion of a shaped element with a thin wall is delicate and can only be carried out at slow speed, which is not very compatible with productivity-related preoccupations. For an assembly technique of welding, in particular, spark welding, it is difficult to obtain an appropriate weld on an extremely thin wall.
With respect to the annular groove where the tire is housed, it is known that the tire exerts a relatively substantial outward force due to its inflation. As a result, the wings must be of ample dimensions in thickness.
For these different reasons, there is a current tendency to utilize sectional bars of relatively substantial and regular thickness, with a reinforced lower bridge to assure a good retention of the spokes and a good mechanical linkage between the spokes and the rim.